Download 402 - Sydenham High School

CHAPTER 8
SUMMARY
(Page 402)
Make a Summary
buret
hydrochloric acid • titrant
• standard solution
• known concentration (0.12 mol/L)
• strong acid (high conductivity;
fast reaction)
• 100% ionized (Arrhenius theory)
100%
+
–
• HCl(aq)→ H(aq) + Cl(aq)
stop cock
• > 99% reacted with water
(Brønsted-Lowry theory)
99%
+
–
• HCl(aq) → H2O(1) + H3O(aq) + Cl(aq)
Erlenmeyer flask
• very low pH
+
• pH = –log [H(aq)] = – log 0.12 = 0.92
gripewater • unknown concentration
indicator • endpoint provides empirical
• NaHCO3(s) dissociates
+
•
the acid-base reaction
•
HCL(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)
–
+
+
–
or H3O(aq) + Cl(aq) + Na(aq) + HCO3(aq) →
or
+
–
H2CO3(aq) + Na(aq) + Cl(aq) (total ionic)
+
–
H3O(aq) + HCO3(s) → H2O(l) + H2CO3(aq)
acid
H+
base
base
–
• NaHCO3(s) → Na(aq) + HCO3(aq)
evidence for the end of
–
HCO3(aq)
–
HCO3(aq)
is a (weak) base (here)
is amphiprotic with
conjugate acid-base pairs of
–
HCO3(aq) – H2CO3(aq) (here) and
–
2–
HCO3(aq) – CO3(aq)
acid
proton transfer
conjugate pair
conjugate pair
Reflect on your Learning
Here is an example:
My thinking on what an acid and a base are has changed from an Arrhenius (ionization) concept to a Bronsted-Lowry
(proton-transfer) concept. I still see value in the Arrhenius concept and will continue to use it whenever it is suitable.
I now understand the difference between a strong and weak acid and a strong and weak base. Now I have to remember
to distinguish between strength and concentration. This takes mental effort
The fact that sometimes a chemical can act as an acid in one reaction and as a base in another reaction is interesting.
I now see how important empirical evidence is to the study of chemistry. The ultimate way of knowing in chemistry is
empirical, not theoretical as I had previously thought. Now I see where chemical knowledge really comes from. This is
what is exciting to me.
Titrations are neat. I especially like the sudden colour change at the endpoint, although I often overshoot the endpoint.
What I don’t understand is how to choose the right indicator from that long list at the end of the book, and how do indicators work anyway? Why do they change colour?
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Unit 3 Solutions and Solubility
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